https://en.wikipedia.org/wiki/Immersion_(virtual_reality)#Presence

According to the VR research team at Valve, all of the following are needed to establish presence :
  • A wide field of view
    • starts to work somewhere around an 80°
    • improves significantly at least out to 110°
  • Adequate resolution
    • 1080p seems to be enough
    • 1440p or better yet 2160p would be huge steps up
  • Low pixel persistence
    • 3 ms or less is required
    • shorter persistences will be required at higher pixel densities
  • A high enough refresh rate
    • at 60 Hz low persistence images flicker badly
    • 95 Hz successfully eliminates visible flicker
    • a somewhat lower refresh rate may be adequate
  • Global display (all pixels are illuminated simultaneously)
    • avoids the compression, stretching, and tilting problems that can occur with the more standard rolling display
    • artifacts of rolling display may be largely corrected by adjusting the frame buffer during each frame to
account for eye motion, but that’s not yet proven
    • without eye tracking there will always be failure cases (with rolling displays) and low-latency head-mounted eye tracking is not a solved problem
    • right now global display is the only approach known to work
  • Optics
    • there can only be one or maybe two lenses per eye
    • there’s no way that just one or two lenses can produce ideal VR viewing;
  • Optical calibration
    • a highly accurate process for characterizing the lenses and correcting the rendered image is absolutely essential
  • Rock-solid tracking
    • requires rock-solid head tracking that reports translation - position in x, y and z - as well as orientation
    • tracking accuracy of a millimeter in position and a quarter-degree in orientation
  • Low latency
    • 20 ms motion-to-last-photon works
    • 25 ms may be good enough

What VR Could, Should, and Almost Certainly Will Be within Two Years :
I’ll talk much more about presence later, but, briefly, it’s the sense of being someplace else while in virtual reality; many people feel as if they’ve been teleported. Presence is an incredibly powerful sensation, and it’s unique to VR; there’s no way to create it in any other medium. Most people find it to be kind of magical, and we think that once people have experienced presence, they’ll want it badly.

The DK1 is not good enough to enable strong presence for most people, but Oculus’ new version of the Rift, Crystal Cove, offers higher resolution, lower latency, low persistence, and translation, all of which are key elements of presence, as we’ll see later, so it’s a big step in the right direction.

You see, for latency and bandwidth reasons, presence can only happen with a head-mounted display connected to a device capable of heavy-duty 3D rendering, so there’s no way that TV, movies, streaming, or anything that lacks lots of local compute power is up to the task.

This feeling of being someplace real when you’re in VR is well known to researchers, and is referred to as “presence,” and it’s presence that most distinguishes VR from 3D on a screen. Presence is distinct from immersion, which merely means that you feel surrounded by the image of the virtual world; presence means that you feel like you’re in the virtual world.

Trying to describe presence is bound to come up short – you can only really understand it by experiencing it.

Presence is when, even though you know you’re in a demo room and there’s nothing really there, you can’t help reaching out to try to touch a cube; when you automatically duck your head to avoid a pipe dangling from the ceiling; when you feel uneasy because there’s a huge block hanging over you; when you’re unwilling to step off a ledge. It’s taking off the head-mounted display and being disoriented to find the real world there. It’s more than just looking at someplace interesting; it’s flipping the switch that makes you believe, deep in your lizard brain, that you are someplace interesting. Presence is one of the most powerful experiences you can have outside reality, precisely because it operates by engaging you along many of the same channels as reality. For many people, presence is simply magic.

Different people experience varying degrees of presence in response to our demos; clearly there are significant variations within the population. Responses have strengthened overall as we’ve improved the experience, so we expect presence to become steadily more powerful as VR technology evolves.

Hard-won experience from a lot of R&D and prototyping has taught us that all of the following aspects have to be good enough before a strong sense of presence emerges:
  • A wide field of view
  • Adequate resolution
  • Low pixel persistence
  • A high enough refresh rate
  • Global display
  • Optics
  • Optical calibration
  • Rock-solid tracking
  • Low latency

Presence starts to work somewhere around an 80 degree field of view, and improves significantly at least out to 110 degrees, which is the widest we’ve tested.

We’ve found that 1080p seems to be enough for presence.

We’ve found that persistence of 3 ms or less is required for presence with a 1K x 1K, 110-degree head-mounted display. Shorter persistences will be required at higher pixel densities.

A scene that looks perfect when viewed statically can ripple horribly when you swivel your head from side to side. This destroys presence, and can induce motion sickness almost instantaneously.

We’ve found that we can get presence with tracking accuracy of a millimeter in position and a quarter-degree in orientation, maintained over a volume no smaller than a meter and a half on a side.

I want to emphasize that presence is not a property of any one of the elements I’ve discussed; it’s a property that emerges when all of the elements are good enough.

Presence can’t be induced if even one of the key elements is subpar.

A Wide Field of View High Resolution Compact Virtual Reality Display LeepVR

The angular field of view required to eliminate the windows is about 80 degrees, so any system that provides a field of view less than 80 degrees, in particular any system with an eye lens whose diameter is much less than about twice the distance from the lens to the center of the eyeball, is going to show a stereo window. Such a system fails in a critical way to qualify as immersive virtual reality.

Information From the Periphery LeepVR
The absence of stereo is not a significant loss to the illusion of presence — even when the FOV is only 70 degrees. The wider the field, the greater the illusion of presence — up to that 270° mark. To provide an immersive VR experience, HMDs should show as much of the 270 degree field of view as possible. A large FOV in an orthoscopic rendering provides a greater sense of immersion than stereopsis in a narrow field.

the critical factor for Virtual Reality immersion is the FOV.